The transfer of energy to and from a working fluid typically is accomplished under the control of a condition sensing device such as a temperature responsive unit or a pressure responsive unit. Ordinarily, the condition responsive means measures a single condition of the working fluid and in turn controls the rate of transfer of energy to or from the working fluid in proportion to the deviation from a set point. This type of control system typically has a proportional offset which is an offset from the desired setpoint or control point established for the operation of the system.
In many systems, there is a minimum or fixed lowest possible energy transfer rate for the system. Above that minimum rate, the system typically can modulate continuously to some fixed upper limit. There are often startup energy losses associated with the transition between a complete off state and the lowest operating rate, each time the system is caused to cycle there can be significant startup losses.
The startup losses, and the operation of the system with a proportional offset, typically leads to certain inefficiencies. A more efficient manner of operating such a system can be brought about by minimizing the number of startup times for the system, and by tailoring the operation of the control so that the working fluid is not over heated or cooled to supply just the minimum amount of energy required to satisfy a particular load.
While the present description deals generally with condition control systems, a detailed description of a prior art type of condition control system will be described in the section of the application entitled "Description of the Preferred Embodiment" with reference to certain of the Figures which will be identified as prior art. This description will establish clearly what the prior art is, and will show why that type of prior art control system is deficient as relates to an efficient manner of operating a condition control system. The system that will be described will specifically be a boiler supplying steam to a steam heated load in response to a fuel burner control system even though any system that controls the transfer of energy to and from a working fluid in a similar manner would benefit from the present invention.